As with any social networking site, be it Facebook, or Myspace, or Twitter, it may be used with two motives.
The first motive being to stay in touch with people, and to have contact with people. This is usually not the sole motive, however. This may also tie in with the other motive.
Social status. Yes, that is the ulterior motive. It's a way of affirming and asserting their social status. You see, with statuses and Twitter, you can notify everyone that you are having a good time, and that you have a life. These two things are central to being "popular," but even more important to being popular are the ranking friends. With wall posts where your ranking friends can write, "You're awesome, lets hang" or a reference to an inside joke, it will be transparent to see that one is a member of the Dominant Culture. This, of course, is not the only way to let everyone know that you have friends and a life--pictures are important. Now, they make sure to only take a couple per hang out session to say, "I'm having so much fun--just look at my silly face!--but I'm having so much fun, that I didn't want to waste more than a few moments taking pictures." It's not a tough language to decipher.
People do the second thing whether they know it or not. Most people are either trying to infiltrate the Dominant Culture, convince others that they've infiltrated the dominant culture, or asserting that they are apart of the Dominant Culture.
Theory #3 of Freshman Culture, Behavior, and Interaction: The members of the Dominant Culture assert their membership through publicly displayed social interaction, while others use this to their advantage in order to project a persona appealing/similar to the members of the DC.
Your Sociologist Blogger,